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Explosive beginnings of a supernova spotted for the first time

Astronomers witnessed the infancy of one of the most spectacular sights in the universe. Amy Middleton reports.

iPTF13dqy (SN2013fs) exploded in a relatively nearby (~160 million light years) spiral galaxy on 6 October 2013 and was detected by the Palomar Transient Factory sky survey a mere three hours after explosion.

Ofer Yaron

An extremely rare recording of a massive star’s explosive death reveals clues about the formation of supernovae.

Reported in Nature Physics by a team led by Ofer Yaronof at the Weizmann Institute of Science in Israel, recent spectroscopic imaging captured the spectacular transformation of a star assumed to have been a red supergiant into a supernova, just three hours after it began.

It marks the first time a supernova has ever been seen in its infancy. Previously observed supernova – the predicted end-point for around 50% of supergiant stars – have all been recorded after the metamorphosis had been underway for several days, meaning that information about the start of the process was already destroyed.

The most recent event, capturing the fiery death of a star dubbed iPTF 13dqy, was captured by the Intermediate Palomar Transient Factory, an automated astronomical survey from Palomar Observatory in California, which has been monitoring the sky since 2013.

The survey snaps two images per night, over an hour period or longer, of a particular astronomical field and then compares them to identify any transient events. Any flagged are then confirmed and examined by a team of researchers.

Red supergiant stars themselves are not difficult to locate because they tend to stand out. They are 10 to 70 times the size of the sun and can be hundreds of thousands of times brighter. They pay for their extravagance, however, burning all their fuel and going nova between a couple of hundred thousand and 30 million years after forming.

That said, and the universe being an enormously large sort of place, picking the ones set to explode is extremely difficult.

“Statistically, it is very likely that not even a single star that is within one year of explosion currently exists in our galaxy,” the researchers explain in their paper.

The team’s analysis shows that before its death, iPTF 13dqy was surrounded by a cloud of gaseous matter, possibly ejected from its core in the last months before its explosion.

“The finding that the probable red supergiant […] ejected material at a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may be common among exploding massive stars,” the researchers write.

“Future flash-spectroscopy observations of a larger sample of events would allow us to determine exactly how common this phenomenon is, placing stronger constraints on the final stages of massive-star evolution.”